Signal processing methods which determine the time-of-arrival of signals are well known. It is known to read frequency modulated coded signals and to determine a time of arrival of these signals to the time resolution given by the inverse of the bandwidth of the signal. To date, no signal processing methods and apparatuses have been described which can improve upon this resolution by analysing the signal in terms of its composite components.
Packet switching networks are known such as modacom and Mobitex. These networks are exclusively operated as messaging networks and they operate according to a structured protocol in which remote units request transmission windows to communicate with the nearest processing base station. The transmitted data packets are of very short duration and each comprises identification code information identifying the unit from which the message was sent. To date, no methods have been proposed to analyse the signals transmitted by remote units operating in accordance with said packet switching networks and thus provide a positioning capability to the packet switching network's messaging capability.
Conventional networks determine the approximate location of GSM telephones and personal message pagers to the resolution of a cell based upon the signal strength of their transmissions. Communication channels are allocated to that base station which receives the strongest signal from the transmitting unit. Conventional networks do not process signals to determine the location of transmitting units to a high resolution.
Furthermore, no signal processing system is presently available which serves to analyse a discrete signal in terms of its composite components and thereby greatly improve upon the bandwidth limitation on the determination of the time-of-arrival of the signal whereby a coded signal can be determined to a time resolution given by the inverse of the bandwidth. Moreover, no signal processing system of this type is known which also serves to determine the position of a remote transmitting unit by differential comparison of the time-of-arrival of the signal at a plurality of receivers in such a simple and effective manner as herein proposed